Vegetables may be subjected to a heat treatment prior to consumption or further processing. Roasted vegetables are used as ingredients for some types of ready-to-eat packed sandwiches which have a shelf life of several days. Roasting, however, by damaging the cell structure makes heat-treated vegetables prone to shrinking and discolouration which limits their storage time. Microbial spoilage of the vegetable matter in the period between agricultural production and consumption of the sandwich is another concern. It would be convenient when the roasted vegetables could obtain an extended storage time during which their good taste and appearance could be retained and microbiological safety could be ensured.
Many methods are known in the art that extend the closed shelf life of vegetables. These methods mainly comprise storing the vegetables in preserving liquids. These liquids contain relatively high levels of salt and/or are very sour. This has a severe and adverse impact on the taste of the vegetables. While a salty or sour taste is quite normal for pickled vegetables, it is not acceptable for the heat-treated, particularly the roasted sandwich vegetables, which should have a rather mild taste. The use of those salty or sour preserving liquids may allow a one year preservation time, but the taste of the preserved heat-treated vegetables has been deteriorated and is much different from the taste of freshly roasted or grilled vegetables.
U.S. Pat. No. 5,925,395 describes methods for preserving fresh vegetables wherein fresh vegetables are cut and exposed to a preserving aqueous solution comprising 0.1-10 wt. % of calcium ions and 0.1-30 wt. % of ascorbate ions or erythorbate ions. Storage without losing fresh taste, appearance and crispiness is claimed for up to 10 days. This method relates to vegetables that apart from being cut have not been further processed, anyway have not been roasted or otherwise heated.
The fresh vegetables described in WO96/14760 are kept in a film, which contains a marinating agent, comprising vinegar, sugar, salt, flavourings and others. This method does not relate to vegetables that have been heat-treated.
Roasted vegetables belong to the ingredients of certain food products, especially packed ready-to-eat sandwiches. For this application the heat-treated vegetables need an extended shelf-life during which their appearance and taste are closely resembling the appearance and taste of freshly heat-treated vegetables.